Gravimetric blender with power hopper cover

ABSTRACT

A gravimetric blender has a frame; a resin material storage hopper supported by the frame, including a hopper cover; a weigh bin located below the hopper for receiving resin material from the hopper downwardly discharging the bin contents after the contents have been weighed; a load cell, connecting the frame and the weigh bin, for sensing weight of the weigh bin; a mixer connected to the frame, below the hopper, for mixing received contents of the weigh bin; and a guide connected to the frame, for movement of the hopper cover therealong.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to machines for processing plasticresin material prior to molding or extrusion, and specifically relatesto gravimetric blenders. Gravimetric blenders are disclosed in U.S. Pat.Nos. 6,007,236; 6,188,936; 6,402,363; 6,467,943 and D424,587, thedisclosures of all of which are incorporated herein by reference.

2. Description of the Prior Art

Many if not most gravimetric blenders operate with vacuum powered orother loaders that downwardly feed plastic resin material into one ormore of the hoppers of the gravimetric blender, where the loaderstypically are positioned on the top of the associated hoppers of thegravimetric blender. Vacuum loaders are disclosed in U.S. Pat. Nos.6,089,794 and 7,066,689, the disclosures of both of which areincorporated herein by reference.

Older gravimetric blenders and many newer larger gravimetric blenders donot have removable hoppers; some small modern gravimetric blenders haveremovable hoppers. But even if removable, the hoppers cannot be removedif a vacuum loader is on top of the hopper, since the vacuum loaderweighs a substantial amount, especially when filled with granular resinmaterial.

Maguire Products, Inc. offers small capacity gravimetric blenders havingremovable hoppers. These small blenders with their necessarily smallerhoppers that are removable from the blender facilitate easy cleanout ofthe hopper by allowing removal of the hopper from the blender. A smallgravimetric blender with a removable hopper is disclosed in U.S. Pat.No. 6,467,943.

If a gravimetric blender hopper has one or more loaders mounted on thehopper lid and the hopper is removable from the blender, presence of theloader(s) on the hopper lid limits, and in some cases may eveneliminate, a worker's ability to remove the hopper from the gravimetricblender. A loader typically has a resin material feed line connected toit and is heavy. Vacuum loaders may weigh from 30 to 50 pounds each,making it awkward and sometimes dangerous for a worker to remove aloader from its position on the gravimetric blender hopper lid.

Moreover, the blender hopper top and hence the loader(s) are typicallypositioned high above the work floor, well beyond a worker's reachwithout using a ladder or a movable platform. This typical positioningof equipment in a plastic resin processing, molding or extrusionfacility, cries for an easy way to move the loader(s) away from thehopper(s), in order to allow removal of the hopper(s) from the blenderfor cleaning and maintenance, without first having to remove theloader(s) from the hopper(s), by lifting the loader(s) off the hopperlid.

A previous approach to this problem has been to place a loader on amount pivotally supported by a post, so that the loader can be swiveledout of the way by pivoting the mount around the post. Sometimes the postand mount are built with a cam or other apparatus so that a slight liftof the mount occurs on initial pivoting, to allow clearance for theloader when rotating sideways on the mount, out of the way of the hopperlid. The support post must be very substantial. The support post mustadditionally be fixed to a very substantial part of the gravimetricblender frame or fixed to the injection molding press or extruder towhich the gravimetric blender is mounted, or even fixed to the facilityfloor, in order to support the loader.

SUMMARY OF THE INVENTION

This invention provides a new approach to the on-going problem in theprior art, as described immediately above. This invention raises thecover or lid (the two terms are synonymous as used herein) on thehopper(s) of the gravimetric blender, raising the cover high enough toallow removal of the hoppers underneath the lid. The invention maintainsall loaders, vacuum powered and otherwise, as well as all weightassociated with the loaders, mounted on the hopper cover, centered overthe blender. The invention does not rotate the loaders to one side. Theinvention provides a simple, more stable, lower cost, safer means fordealing with the problem of heavy loaders resting on lids of gravimetricblender hoppers, whether or not the hoppers are removable from theassociated gravimetric blender.

The invention controls the height to which the blender lid is raised byselection of the stroke length of pneumatically powered piston-cylindercombinations that raise the lid from the hoppers. Weight liftingcapacity according to the invention is desirably set by the diameter ofthe cylinders of the piston-cylinder combinations. An air switch isdesirably used to actuate the cylinders and thereby raise and lower thehopper lid. Any unbalanced load is handled by a center telescoping rod,which serves a part of a guide, keeping the hopper lid flat and in ahorizontal position, regardless of any offset of the weight of loadersor any imbalance of the pneumatic pressures actuating thepiston-cylinder combinations.

The rod desirably extends downwardly from the center of the lid,desirably into a fixed vertical tube. At one end the rod is preferablyvery rigidly attached to the hopper lid. The rod telescopes upwardly outof the tube, remaining vertical, thereby assuring that the lid remainshorizontal, when the lid is lifted from the hoppers by actuation of thepneumatically powered piston-cylinder combinations.

Accordingly, in one its aspects this invention provides a gravimetricblender having a frame, at least one resin material storage hopper atthe top of the frame including a hopper cover, a weigh bin preferablylocated within the frame, positioned below the hopper and adapted fordownward discharge of bin contents after the contents have been weighed,at least one load cell connecting the frame and the weigh bin forsensing weight of the contents of the weigh bin, a mixer below the weighbin for mixing contents of the weigh bin after the weighed contents falldownward from the weigh bin to the mixer, and a guide adapted forvertical movement of the cover for the hopper(s) therealong between aposition at which the cover contacts and thereby closes the hopper(s)and a position at which the cover is spaced vertically above thehopper(s), whereby the hopper top(s) are open. The invention furtherpreferably includes means for moving the hopper cover along the guide.

The invention still further preferably includes at least onepiston-cylinder combination with one of the piston and the cylinderbeing connected to the blender frame or some other suitable part of theblender, and the other of the piston and the cylinder being connected tothe cover, with the combination serving to move the hopper coververtically along the guide.

In another aspect of the invention, the invention may further include apair of piston-cylinder combinations, each of the combinations havingeither the piston or the cylinder connected to the blender frame or tosome other suitable part of blender, and the other of the piston and thecylinder connected to the cover, for moving the hopper cover verticallyalong the guide, wherein the piston cylinder combinations are on eitherside of the guide.

The guide is preferably located along a vertical central axis of theframe.

The invention may further include a connector in the nature of anelongated sleeve desirably connected to the cover and positioned betweenthe cover and the guide, for ensuring maintenance of the cover in ahorizontal position as the cover moves vertically along the guide.

In yet another of its aspects this invention provides a method forremoving a gravimetric blender hopper, having a cover verticallysupporting a vacuum loader or other equipment for feeding resin materialinto the hopper, from the blender, for cleaning, material changeover andthe like, where the method includes advancing the hopper cover upwardlyfrom the hopper along a vertical guide by application of pneumaticpressure to a piston-cylinder combination, with one of the piston andcylinder connecting with the cover and the other of the piston andcylinder connecting with the blender frame, to a position in which thecover is sufficiently remote from the hopper that a worker can accessthe coverless hopper and disconnect the hopper from the blender frame,while maintaining the hopper cover in a horizontal orientation tocontinue supporting the vacuum loader or other equipment for feedingresin material into the hopper. The method in this aspect yet furtherincludes advancing the hopper while applying pneumatic pressure to apair of piston-cylinder combinations, one each of the piston andcylinder of the combinations connecting to the cover and the other ofthe piston and the cylinder of the combination connecting to the blenderframe. In this aspect of the method, advancement of the hopper coverfurther includes moving the hopper cover slidably along a verticalguide.

In still yet another aspect of the invention, there is provided a methodfor removing a gravimetric blender hopper, having a cover verticallysupporting a vacuum loader or other equipment for feeding resin materialinto the hopper, from the blender for cleaning, material changeover andthe like, where the method includes advancing the hopper cover upwardlyfrom the hopper slidably along a vertical guide to a position at whichthe cover is sufficiently remote from the hopper that a worker canaccess the coverless hopper and disconnect the hopper from the blenderframe, where the method further includes maintaining the hopper cover ina horizontal orientation to continue support of the vacuum loader orother equipment for feeding resin material into the hopper. In thisaspect of the invention, the advancing may be performed pneumatically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a gravimetric blender with a power hoppercover in accordance with the preferred embodiment of the invention, withthe hopper cover shown in a down position, with the hoppers resultantlyclosed.

FIG. 2 is a front view, taken similarly to FIG. 1, of a gravimetricblender with a power hopper cover in accordance with the preferredembodiment of the invention, with the hopper cover shown in a raisedposition, with the hoppers resultantly open.

FIG. 3 is a front view of a gravimetric blender having a power hoppercover in accordance with the invention, with the view taken similarly toFIGS. 1 and 2, with resin loading apparatus depicted in place on thehopper cover, with the hopper cover shown in a down position, with thehoppers resultantly closed.

FIG. 4 is a front view of a gravimetric blender having a power hoppercover in accordance with the invention, with the view taken similarly toFIGS. 1, 2 and 3, with resin loading apparatus depicted in place on thehopper cover, with the hopper cover shown in a raised position, with thehoppers resultantly open.

FIG. 5 is an isometric view of a gravimetric blender with a power hoppercover in accordance with the invention, with resin loading apparatusdepicted in place on the hopper cover, with the hopper cover shown in araised position and with the hoppers resultantly open, illustrating aworker having removed a hopper from the gravimetric blender for materialrefill, changeover or maintenance purposes.

FIG. 6 is an enlarged broken isometric view of the upper portion of agravimetric blender having a power hopper cover in accordance with theinvention, with the hopper cover shown in a raised position with thehoppers resultantly open, where the view has been taken at a positionsimilar to FIG. 5 but closer to the blender, so as to show more detail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE KNOWN FORPRACTICE OF THE INVENTION

Referring to drawings in general and to FIGS. 1 and 2 in particular, agravimetric blender is designated generally 10 and includes a hopperassembly 11 having a plurality of hoppers, which are individuallydesignated generally 12. The hoppers 12, each of which is preferablyindividually manually removable from blender 10 without use of tools,are supported by a frame designated generally 14.

In a typical gravimetric blender such as that illustrated, frame 14supports, directly or indirectly, a weigh bin 15 into which portions ofsolid granular plastic resin material or other granular or powderymaterial can be metered and then weighed prior to release into a mixchamber. The mix chamber is preferably positioned immediately below theweigh bin to receive the weigh bin contents when the weigh bin isdumped, opened or otherwise manipulated so as to drop the material thathas been weighed into the mix chamber. The mix chamber is designatedgenerally 20 in the drawings. A rotatable agitator on a shaft providesthe mixing mechanism, which agitator is configured much like a beater ina home food mixer and which is desirably positioned within mix chamber20 for rotation therein to blend the contents of weigh bin 15 asreceived by mix chamber 20.

Frame 14 may include four upstanding side panel members. In onepreferable construction frame 14 is steel and is formed from a singlesheet, bent to form three sides, as disclosed in U.S. Pat. No.6,467,943. Alternatively, the blender frame may be constructed usingsteel angle members positioned at each of four corners to define theframe.

Hopper assembly 11, with the desirable plurality of hoppers 12, allows aplurality of different solid resinous materials to be dispensed from theindividual hoppers 12 into weigh bin 15 by suitable valve mechanisms,which are desirably located within and proximate to the bottom of agiven hopper 12. The hoppers 12 are preferably individually manuallymountable on and removable from frame 14 of gravimetric blender 10.

Preferably located close to the top or upper extremity of frame 14 areoutwardly flared guide flaps 34, with one guide flap on each of the foursides of the frame. In the hopper configuration illustrated in U.S. Pat.No. 6,467,943, where the frame 14 is fabricated from a single sheet bentto form three sides, three outwardly flared guide flaps 34 result. Inthat construction, outwardly flared guide flaps 34 are integral with andformed as a part of the solid side panels by bending the upwardextremities of the solid side panels substantially into the shapeillustrated in FIG. 1. In that construction a fourth outwardly flaredguide flap is positioned above a fourth panel, which is a transparentremovable front panel, with the fourth outwardly flared guide flap beingwelded to the upward extremities of two solid side panels forming a partof frame 14.

Gravimetric blender 10 further includes preferably at least one loadcell used to determine the weight of the contents of weigh bin 15, andwhich desirably connects weigh bin 15 to frame 14. The load cellillustrated in FIG. 1 is typical and designated 32.

A pneumatically actuated piston-cylinder combination 132 may be used tomove a desirably pivotable bottom portion of weigh bin 15, thereby tocause the contents of weigh bin 15 to drop therefrom into mix chamber20.

Still referring principally to FIG. 1, gravimetric blender 10 includes ahopper cover 38 positioned above hopper assembly 11 and movablevertically in a manner so as to close the hoppers 12 of hopper assembly11 when hopper cover 38 is in a lower position, and to open and therebypermit access to individual hoppers 12 of hopper assembly 11 when hoppercover 38 is in a raised position, remote from hoppers 12 of hopperassembly 11. In FIG. 1 gravimetric blender 10 is illustrated with hoppercover 38 in position on the top of and contacting hoppers 12, therebycovering the hoppers 12 of hopper assembly 11 and precluding access tothe interior of hoppers 12 and further essentially precluding removal ofhoppers 12 so long as hopper cover 38 is in the position illustrated inFIG. 1.

In FIG. 2 gravimetric blender 10 is illustrated with hopper cover 38raised from the position illustrated in FIG. 1, with hopper cover 38 nolonger covering hoppers 12 of hopper assembly 11, thereby permittingaccess to individual hoppers 12 from the top thereof and permitting easyremoval of individual hoppers 12 from gravimetric blender 10.

Hopper cover 38 is moved vertically by action of at least one anddesirably a pair of piston cylinder combinations designated generally 46in FIGS. 1 and 2. Only one piston-cylinder combination of the pair isvisible in FIGS. 1 and 2 since the pair of piston-cylinder combinations46 are aligned with and positioned on either side of a vertical guidefor hopper cover 38, where the vertical guide is designated 40 and isshown in FIGS. 5 and 6. The second piston-cylinder combination 46 isimmediately behind and therefore hidden by the first piston-cylindercombination 46 visible in FIGS. 1 through 4.

Load cell 32, weigh bin 15 and pneumatic piston-cylinder combination132, shown in FIG. 1, are not illustrated in FIGS. 2 through 4 toenhance drawing clarity.

As further shown in FIGS. 1 and 2, hoppers 11 may have inspection portsformed therein. Additionally, guide flaps 34 may also be apertured so asto provide access to the inspection ports. The inspection ports in FIGS.1 and 2 have been numbered 134. Inspection ports 134 are typically sightglasses installed in the hopper walls with suitable gasketingsurrounding the sight glasses. Only some of the inspection ports 134have been numbered in FIGS. 1 and 2 in order to enhance drawing clarity.

As apparent in comparing FIG. 1 and FIG. 2, when piston-cylindercombinations 46 are unactuated, with piston rods 52 of piston-cylindercombinations 46 within the cylinders 50 of piston-cylinder combinations46, as illustrated in FIG. 1 where piston rod 52 substantially cannot beseen due to being within cylinder 50 of piston-cylinder combination 46,the hopper cover 38 is in a lower position, where it may contact andclose the open tops of hoppers 12 comprising hopper assembly 11. Whenpiston-cylinder combinations 46 have been actuated and piston rods 52have extended therefrom as illustrated in FIG. 2, this lifts hoppercover 38 from the hoppers 12, where the upper edges of the hopper wallshave been designated 136 in FIG. 2. This lifting action is effectuatedas a result of the cylinder portions 50 of piston-cylinder combinations46 being fixedly connected by their nose mounts to hopper cover 38. Thepiston-cylinder combinations are upside down relative to conventionalpositioning and usage of such piston-cylinder combinations.

Referring to FIGS. 3 and 4, the gravimetric blender depicted in FIGS. 1and 2 is shown again with the gravimetric blender in FIG. 3 being inessentially the same configuration as the gravimetric blender of FIG. 1,that is with the hopper cover 38 preferably contacting the upperextremities 136 of hoppers 12 thereby closing hoppers 12 and precludingaccess to the interior of hoppers 12 and also essentially precludingremoval of hoppers 12 from gravimetric blender 10. FIG. 4 is similar toFIG. 2 in that it depicts hopper cover 38 raised from and no longercontacting upper extremities 136 of hoppers 12 so that an operator mayhave access to the interior of hoppers 12 and may remove one or morehoppers 12 from gravimetric blender 10. As noted above, in FIGS. 3 and4, similarly to FIG. 2, weigh bin 15, piston-cylinder combination 132which dumps weigh bin 15, and load cell 32 have not been illustrated toenhance drawing clarity.

In FIG. 3 a vacuum actuated resin loader of the type disclosed in U.S.Pat. Nos. 6,089,794 and 7,066,689 and which is available from MaguireProducts, Inc. in Aston, Pa., is depicted mounted on the upper surfaceof hopper cover 38. Additionally, a generic material loader has alsobeen depicted mounted on the upper surface of hopper cover 38, where thegeneric material loader is designated 36A.

Vacuum actuated resin loader 36 receives granular resin material throughan inlet port designated generally 148 in the drawings, with granularresin material filling a receiver designated generally 104 in thedrawings. Resin loader 36 provides granular resin to the particularhopper 12 located immediately below resin loader 36 upon opening of asuitable, preferably pneumatically powered, valve, typically in the formof a slide gate, which has been designated generally 198 in thedrawings. The piston-cylinder combinations that are desirablypneumatically powered and which operate the slide gate valve 198 at thelower extremity of loader 36 are illustrated in FIG. 5 and designatedgenerally 200.

Referring to FIG. 5, where a worker's hands are shown, with the workerhaving removed one of hoppers 12 from gravimetric blender 10, hoppercover 38 is illustrated in the raised position with two resin loaders 36illustrated mounted on hopper cover 38 and a generic loader 36A is alsoillustrated mounted on hopper cover 38. In FIG. 5 it is apparent thatthe resin loader 36 illustrated closest to the viewer, is the loader forthe hopper 12 that has been removed from gravimetric blender 10, andthat the remaining resin loader 36, to the left in the drawing, is theresin loader servicing the hopper 12 remaining mounted on gravimetricblender 10, where this hopper 12 is on the left hand side of thedrawing.

FIG. 5 further illustrates that there are two piston-cylindercombinations 46 used to raise and lower hopper cover 38. While only onepiston-cylinder combination 46 is visible in FIG. 5, two piston rods 52,one for each of the piston-cylinder combinations 46, are illustrated.Additionally, located desirably at the center of hopper cover 38 andpositioned essentially at the center and preferably running along acentral vertical axis of blender 14, is a vertical guide, designatedgenerally 40, for hopper cover 38 as hopper cover 38 goes up and downunder the influence of pneumatic piston-cylinder combinations 46.Vertical guide 40 includes two parts, a tube 42 that is secured to frame14 of gravimetric blender 10, and a rod 44 that telescopes slidablywithin tube 42 and is fixed to hopper cover 38. The sliding, telescopingarrangement of vertical guide 40, with tube 42 slidably receiving rod44, is best seen in FIG. 6, which is drawn to a larger scale than FIG.5.

Referring to FIGS. 5 and 6, two separation plates 58, only one of whichis fully illustrated in FIGS. 5 and 6, extend in opposite directionsaway from the central vertical axis of blender 10, with each separationplate 58 forming a part of the structure for receiving a respectivepiston rod 52 associated with a respective piston-cylinder combination46. Separation plate 58 illustrated in FIGS. 5 and 6 connects to a strap60 which has an angled portion 62 and a vertical portion 64, asillustrated in FIG. 6. The connection of separation plates 58 to strap60 may be by welding or via suitable screw-nut-angle combinations.

Separation plate 58 connects with and holds tube 42 of vertical guide 40via conventional circular clamps 56, which wrap around the outside oftube 42 and tighten thereabout when clamps 56 are secured to separationplate 58 by suitable screw-nut combinations. The screw-nut combinationsare not numbered to enhance drawing clarity. Three such circular clamps56 are illustrated in FIG. 6.

With continued reference to FIG. 6, hopper cover 38 has a plurality ofapertures, two of which are shown in FIG. 6 and designated generally 68,for flow downwardly of granular resin material from the resin loaders 36mounted on the top of hopper cover 38, into individual hoppers 12. InFIG. 6 an aperture 68 is illustrated on the left-hand side, in positionto facilitate downward flow and fill of the hopper 14, which has beenremoved from gravimetric blender 10 as illustrated in FIG. 5. A secondaperture 68 is also illustrated in hopper cover 38, at a position tofacilitate filling of hopper 12 appearing on the left-hand side of FIG.6.

Typically, valves for permitting and halting downward flow of resinmaterial from loader 36 are a part of a loader 36 and are actuated bypneumatic piston-cylinder combinations forming a part of loader 36;these piston-cylinder combinations have been designated 200 and arevisible in FIG. 5. Bolts and nuts secure resin loaders 36 to the uppersurface of hopper cover 38. The bolts extend through hopper cover 38 andare secured by suitable nuts; neither have been illustrated in FIG. 6 inorder to enhance the clarity of the drawing.

Generally rectangular, hollow, somewhat elongated hopper support boxes64 are preferably secured to each separation plate 58 by suitablenut-bolt combinations as illustrated in FIG. 6. Hopper support box 64 iselongated in a direction parallel with the associated separation plate58, running transversely to vertical guide 40. Hopper support box 64includes suitable apertures 68 formed as slots opening in the upwardlyfacing surface of hopper support box 64, which upwardly facing surfaceis not numbered in FIG. 6, and extending downwardly in a lateral surfaceof hopper support box 64, which also is not numbered in FIG. 6 but whichfacingly contacts a hopper 12 when a hopper 12 is in position. Hopper 12desirably is equipped with bolts extending outwardly therefrom, asillustrated in FIG. 5, so that the bolt heads, or engaged nuts, may fitinto and slide downwardly within the slots 70 in hopper supply box 64.This provides added vertical support for hoppers 12 when in place withingravimetric blender 10 and lends rigidity to the entire assembly ofseparation plate 58, strap 60, vertical guide 40 and piston rods 52.

The extremities of piston rods 52 that are remote from driving pistons48 resident within cylinders 50 of piston-cylinder combinations 46, aresecured to separation plate 58 via rod receptacles 72 that retain theextremity ends of piston rods 52 and are preferably secured toseparation plate 58 by suitable nut-bolt combinations. Accordingly,since separation plate 58 is connected to guide flap 34, which is a partof frame 14 of gravimetric blender 10, and since rod receptacle 72 isfixed to separation plate 58, actuation of piston-cylinder combinations46 and resultant extension of piston rod 52 pushes hopper cover 38, andall of the structures, including the resin loaders, supported by hoppercover 38 upwardly as piston rods 52 extend from piston-cylindercombinations 46 through nut-bushing combinations 54.

As illustrated in FIG. 6, hopper cover 38 includes a downwardlyextending lip 66 preferably extending around the entire periphery ofhopper cover 38.

The height to which piston-cylinder combinations 46 raise hopper cover38 from the upper edges 138 of hoppers 12 is controlled by the strokelength of piston-cylinder combinations 46. The weight lifting capacityis established by the inner diameter of cylinders 50 of piston-cylindercombinations 46.

An air switch is used to actuate the piston-cylinder combinations 46 andthereby raise hopper cover 38. Any imbalance in the load presented byhopper cover 38 and the resin loaders and other items which may besupported by hopper cover 38 is handled by the guide 40 consisting ofrod 44 telescoping into tube 42. The presence of vertical guide 40together with the two piston-cylinder combinations located on eitherside of guide 40, with guide 40 being in alignment with the piston rods52 of piston-cylinder combinations 46, serves to keep hopper cover 38flat and horizontal regardless of any offset in the load carried byhopper cover 38 and regardless of any imbalance in the supplied airpressure as between the two piston-cylinder combinations 46.

Rod 44 is rigidly attached to blender cover 38. Since rod 44 telescopesupwardly out of tube 42, that action together with the rigid connectionof rod 44 and hopper cover 38, with rod 44 being oriented transverselyto hopper cover 38, assures that hopper cover 38 remains horizontal.Furthermore, vertical guide 40 helps to handle any unbalanced load inthe event one occurs and serves to keep blender cover 38 flat in theevent of an offset in the pneumatic pressures applied to piston-cylindercombinations 46.

With the invention, unlike prior gravimetric blenders, the hopper coveris preferably not supported by the hoppers. Rather, the hopper cover ispreferably supported by the piston rods 52 being mounted via rodreceptacles 72 to separation plates 58 and hence to frame 14. In otherwords, hopper cover 38 goes up and down, and when down may contact theupper extremities 136 of hoppers 12, but hopper cover 38 preferably doesnot rest on hoppers 12 even when hopper cover 38 is in contact withhoppers 12.

With the two piston-cylinder combinations 46, one on either side of thevertical guide, the invention can be operated to lift the hopper cover38 two inches, four inches, six inches or whatever height is required.All that need be done is to change out one set of piston-cylindercombinations and replace with a second set of different size, to provideany required different lift height. Not only does the power hopper cover38, when at its extreme vertical upward position, provide clearance forhopper removal, this also provides easy cleaning of the bottoms of resinloaders 36.

Desirably, rod receptacles 72 receive a clevis connected to the end ofpiston rod 52, with rod receptacles 72 including a pin connection of theclevis to the separation plate 58, which is located between adjacenthoppers 12 and which becomes the support for the hopper cover and theloaders mounted on the hopper cover, as discussed generally above.

In FIG. 6, the structure, particularly the bolts and nuts securing resinloaders 36 to the upper surface of hopper cover 38, which securingstructure would be visible looking at the lower or bottom surface ofhopper cover 38, has not been shown in order to enhance drawing clarity.

Another factor making the resin loaders difficult to handle andsometimes dangerous to remove, is that the resin loaders usually havematerial lines connected to them. As a result, to remove a loader fromthe gravimetric blender, it might be necessary either to disconnect thematerial line, thereby requiring a worker to make provision for thematerial that will be spilled from that line, or to leave the lineconnected to the loader as the loader is lifted off the hopper cover. Ifthe line remains connected, this makes the job of removing the loadereven more difficult since the lifting is more awkward with the materialline attached. Additionally, the loader would being even heavier andtherefore more difficult to handle than usual.

1. A gravimetric blender comprising: a) a frame; b) a resin materialstorage hopper supported by the frame, including a hopper cover; c) aweigh bin located below the hopper for receiving resin material from thehopper and downwardly discharging the bin contents after the contentshave been weighed; d) a load cell, connecting the frame and the weighbin, for sensing weight of the weigh bin; e) a mixer connected to theframe, below the hopper, for mixing received contents of the weigh bin;and f) a guide connected to the frame, for movement of the hopper covertherealong.
 2. The blender of claim 1 in which the cover is movablealong the guide between positions at which the cover contacts andthereby closes the hopper and at which the cover is spaced from thehopper and the hopper is open.
 3. The gravimetric blender of claim 1 inwhich the guide is adapted for vertical movement of the hopper covertherealong.
 4. The gravimetric blender of claim 1 wherein the hoppercover is transverse to the guide.
 5. The gravimetric blender of claim 1further comprising means for moving the hopper cover along the guide. 6.The gravimetric blender of claim 1 further comprising at least onepiston-cylinder combination, with one of the piston and the cylinderbeing connected to the frame and the other of the piston and thecylinder being connected to the cover, for moving the hopper cover alongthe guide.
 7. The gravimetric blender of claim 1 further comprising apair of piston-cylinder combinations, each having one of the piston andthe cylinder connected to the frame and the other of the piston and thecylinder connected to the cover, for moving the hopper cover along theguide, with the piston-cylinder combinations located on either side ofthe guide.
 8. The gravimetric blender of claim 1 in which the guide islocated vertical.
 9. The gravimetric blender of claim 6 wherein thepiston-cylinder combination is pneumatically actuated.
 10. Thegravimetric blender of claim 9 wherein the piston-cylinder combinationmoves the hopper cover away from the hopper upon powered advanced of thepiston within the cylinder and wherein spring return of the piston fromthe advanced position results in the cover returning to contact andthereby close the hopper.
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 24. A method for moving a gravimetric blender hoppercover, supporting a vacuum loader or other equipment for feeding resinmaterial into the hopper, for blender cleaning, material changeover andthe like, comprising advancing the hopper cover away from the hopperalong a guide to a position at which the cover is remote from the hopperso that the requisite blender cleaning, material changeover and the likecan be performed, while maintaining the hopper cover in position tocontinue supporting the vacuum loader or other equipment for feedingresin material into the hopper.
 25. The method of claim 24 in whichmoving the hopper cover further comprises applying fluid pressure to apiston-cylinder combination having one of the piston and cylinderaffixed to the cover and the other of the piston and cylinder connectedto the blender frame.
 26. The method of claim 24 wherein moving thehopper cover further comprises moving the hopper cover along a verticalguide.
 27. (canceled)
 28. In a gravimetric blender including a hopperand a hopper cover, the improvement comprising: a) means for moving thehopper cover towards and away from the hopper; and b) means for guidingthe hopper cover during movement thereof.
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 32. The gravimetric blender of claim 28, furthercomprising means for maintaining the hopper cover horizontal duringmovement thereof.
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